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The Characteristics And Mechanism Of Tight Sandstone Reservoir Of The Fourth Member Of The Upper Triassic Xujiahe Formation At The Fenggu Structure In Western Sichuan Depression

Posted on:2012-03-29Degree:MasterType:Thesis
Country:ChinaCandidate:C F LiuFull Text:PDF
GTID:2210330338968021Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
According to the observation and comparative analyses of the exposure profiles, cores and slices, logging traces and conventionally physical properties of Xujiahe Formation in Fenggu area, etc., the characteristics of the facies, petrology, fractures of tight-sands reservoirs of the fourth member of Xujiahe Formation is identified. Through the analysis of sedimentary facies, lithological composition, diagenesis,tectonism and other aspects, and analytical study and evaluation on the factors influencing the development of tight-sands reservoirs of the Xujiahe Formation fourth member, the favorable sedimentary microfacies, master control factors of reservoir development and the mechanism of the high quality reservoir have been indicated.The formation of the fourth member of Xujiahe Formation in Fenggu Structure, is made up of slightly unequal or isopachous thickness layers of interbeddings of fine-coarse graded lithic (calcarenaceous) sandstone, (pebbled) lithic quartz sandstone, calcarenaceous packsand, (argillaceous) siltstone, dark gray-black (silty) argillutite, bass and so on.The study of paper evidence that the fourth member of Xujiahe Formation is divided into the typical tight-sands reservoir with low porosity and low permeability. The pore space is chiefly composed of cracks and pores and the reservoir type is fracture-pore or pore. The pores mainly consist of intergranular dissolution pores and intragranular dissolved pores, retaining some residual primary intergranular pores, the inferior are moldic pores, intercrystal pores and dissolved fractures, etc..It is concluded in the paper that the fourth member sandstone reservoir of the Upper Triassic Xujiahe Formation of Fenggu Region in the middle section of western Sichuan Depression, generally, is characterized by low porosity and low permeability, strong densification, superpressure, rapid changes in lithofacies and strong heterogeneity, etc.. However, the relatively good porosity and permeability reservoirs (hereinafter referred to as "high quality reservoir") with more than 6% porosity, are still developed in the local, which is mainly composed of mesograin-macrograin lithic (calcarenaceous) sandstone and accessory constituents of mesograin-macrograin lithic silicarenite.The development of the reservoirs is mainly affected by the sedimentary facies and diagenesis. The distribution of the high quality reservoir beds of the fourth member of Xujiahe Formation is controlled by the microfacies. The quality reservoirs in the fourth member of Xujiahe Formation in Fenggu Region develop in thick sandstone formations in the tide-influenced channels, intertidal-subtidal channels, bar, swash bar. In these environments, large thickness of single sand body, low shale index with GR generally between 28-41API, the main lithology of the light gray-gray and mesograin-macrograin lithic(calcarenaceous) sandstone and lithic silicarenite. Favorable sedimentary facies is the premise of high-quality reservoirs. Sedimentary environments and facies by controlling such as original source meterial, hydrodynamic force, determine the sediment composition, grain size, sorting, psephicity, the component of interlayer water and interstitial fluid, thickness and distribution of sands and so on, determined the material basis for the formation of high-quality reservoirs, thereby affecting the diagenesis, diagenesis type, porosity evolution and pore type. Diagenetic evolution and diagenetic grade directly determines the final merits of the reservoirs and reservoir properties in the vertical and horizontal changes. Meanwhile, the evolution of diagenesis is closely related to the structural position of Fenggu structure, maturation of source rocks and the formation of organic acids of the fourth member coal measure strata.The main diagenesises influenced the development of porosity in the Xujiahe Formation fourth member conclude diagenetic compaction-pressolution, carbonate cementation and dissolution. The lithogenous phase of compaction-pressure solution is widely developed in the Xujiahe Formation of the West Sichuan Depression and its strength is mainly affected by depth, in which the location of the foreland belt, rock and mineral composition. Compaction- pressure solution is an important reason for the fourth member of Xujiahe Formation lowering reservoir porosity and densing sands. Carbonate cementation is the main reason for the fourth member to make the porosity lower and the sandstone reservoirs densed. It is divided into the early carbonate cementation and the late carbonate cementation. The formation of protection for the highly porous layers is primarily the early carbonate cementation at the same time when it has a destructive effect on the reservoirs. The late carbonate cementation has a destructive effect on the reservoirs. In Fenggu Structure, dissolution is the main mechanism of developing induced pores and inproving the porosity in the fourth member sandstone reservoir. Denudation is crucial to improve the reservior storage.In addition, the fractures have a relatively greater impact on the reservoir permeability. Multiphase faulting, tectoclases and diagenetic fractures jointly constitute a wide range of fracture network systems, greatly improving the permeability of the reservoir, which is conducive to corroding and expanding corrosion zone, favorable for hydrocarbon migration, reservoir accumulation and adjustment.
Keywords/Search Tags:Western Sichuan Depression, Xujiahe Formation, Sedimentary Facies, Diagenesis, Tight Sandstone
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